1. Field of the Invention
The present invention relates to a vector overmodulation technique with respect to the voltage applied to a motor, and more particularly, to a voltage vector overmodulation technique considering a counter electromotive force of a motor.
2. Description of the Related Art
Microprocessors and logic circuits have become highly integrated and exhibit high performance. With the above developments in the semiconductor technologies, the operational performance and control algorithm used in a power converting apparatus such as an inverter are being developed more intensively. Particularly, as the current control and PWM (pulse width modulation), which are core control technologies for the power converting apparatus, become digitized with their performance increasing, various methods of PWM are currently employed in the industrial field. Of the PWM methods, a spatial vector PWM method in which the rate of voltage use is high and higher harmonics exists less is actively adopted.
An earlier voltage vector overmodulation technique uses a simple algorithm so that vector overmodulation is easily realized and less calculation is required. However, in the earlier voltage vector overmodulation method, the voltage selected by the overmodulation is generated without consideration of the dynamic characteristics of the motor. That is, although the voltage of the motor is constituted by components of a counter electromotive force and a voltage drop due to inductance and resistance, since the earlier technique selects the voltage at the boundary between the command voltage and the side of a hexagon, the counter electromotive force and voltage drop components are not taken into consideration so that an error occurs. Accordingly, a voltage having an error in the transient state is applied to the motor so that the control performance of a motor control system is lowered.